Download DNA Slides - U3A in Kennet

DNA
Deoxyribose Nucleic Acid
The Cell
Between 10 and 100 cells
on one full stop
The Nucleus
contains 23 x 2 chromosomes
One set from each
of your parents
DNA
Deoxyribose Nucleic Acid
These are base pairs CG or AT
¬
Each cell in your body has
3000 million base pairs (x2)
¬
Your body contains about
30,000,000 million (somatic) cells
¬
The DNA from one cell would
stretch out to about 2 meters
ê
Laid out end-to-end all your DNA would stretch
from one side of the solar system to the other
6 times
1000 million nm in 1 meter
DNA
¬
Historic beliefs
¬
Finding the code
¬
How it works (just a hint)
Spermism
or Preformationism
Pythagoras 530 BC
Male makes miniature people
or
Male contains a complete miniature adult
(the humunculus)
Matryoshka dolls
Female role is to protect and nourish
the little people
The perfect
x
EUGENICS
Plato 380 BC
¬
Went further:
If two sides of a perfect
x
are perfect
then so will be the third side
¬
The elite ruling class will ensure only perfect unions
leading to genetic utopia
Epigenesis
Aristotle 350 BC
¬
How come children get traits from grandmothers and mother?
Young men make children, before later life traits develop?
How can males produce females?
¬
De Generatione Animalium the Latin translation of his work of 5
books:
- the 4 causes of existence split between male and female
- male provides initiation instructions (the efficient cause)
- female constructs the being (the material cause)
ê
Human beings are created from instructions.
Preformationism Vs Epigenesis
¬
¬
Two competing theories remained unchanged for next 2000
years
The Church supported Preformationism
Gregor Mendel
“The Father of Genetics”
1822 -1884
¬
Austrian monk and less successful teacher
¬
Peas have simple genetic make-up, easy to crosspollinate or self pollinate
¬
1865 (Shortly after Darwin) Published sets of
rules about inheritance …...
…...and was ignored for the next 30 years.
Rediscovered in 1903.
Mendel's Laws
1
The Law of Segregation
Gene pairs determine inherited traits
and are selected randomly
2
The Law of Independent Assortment
The inheritance of one trait is not dependent
on the inheritance of another
3
The Law of Dominance
If one parent has a dominant gene (AA) and the
other has a recessive gene (aa) the offspring will
have Aa and the traits associated with A
Charles Darwin
1809 -1882
¬
Varied background in geology, natural history,
taxidermy and priesthood training
¬
Joined Beagle voyage (1831-36) as a companion
¬
Transmutation was the popular theory:
- new species arose spontaneously
- which then advanced up the evolutionary ladder
- nervous fluid would cause inheritance and
response to the environment
¬
“On the Origin..” published 1859, did not explicity
cover humans.
Took 50 years for full acceptance.
Finding the Code
The key 20th century discoveries
1919
Phoebus Levene (Russian)
DNA shown to be a series of nucleotides, repeating molecules
of nitogen bases plus sugar and phosphates.
1944
Oswald Avery and colleagues (American)
DNA causes bacterial transformation (genetic alteration) not
proteins.
1950
Erwin Chargaff (Austro-Hungarian → USA)
DNA bases
A (adenine) always = T thymine as a %.
and
G (guanine) always = C (cytosine) as a %.
ê
A always paired with T
G always paired with C
Finding the Code
What was known by the early 20th century
1665
Robert Hooke discovered the cell using the new microscope
1776
Cells not structural but fundamental
1804
Cells not homogenous but individual containing a nucleus
1839
1881
Cells recognised as fundamental building blocks of all life
which contain heredity instructions.
Only cells give rise to other cells.
“Nuclein” discovered inside white blood cells. Acidic and high
in phosphorous, but not a protein. It was DNA.
Chromosomes discovered and recognised as the vectors of
heredity
The five bases in the nucleus discovered – A G C T and U
1909
Concept of a gene – a unit of heritability
1869
1880
Finding the Code
The key 20th century discoveries
May 1952 Raymond Gosling (King's College PhD student)
under the supervision of Rosalind Franklin
Used X-ray diffraction to take a clear pictue of the
structure of DNA. Franklin consigned it to a drawer.
Photo 51
1953
Maurice Wilkins (Kings College) – worked on phosphorescence,
radar, X-ray diffraction producing the first DNA images in 1951.
Was shown the Gosling image and showed it imprudently to
James Watson.
Finding the Code
The key 20th century discoveries
1953
James Watson working with Francis Crick
(Cambridge)
- were working on the incorrect Linus Pauling model of
DNA (triple helix) until they saw Photo 51
Key insights:
The DNA backbone was a double helix
The bases A and T, and C and G which are joined by a
hydogen bond are the same length
Which means the bases can fit inside the double
backbone structure
HOW IT WORKS
The code is read sequentially along one strand in triplets
known as codons:
Each codon controls the making of an amino acid.
There are 23 amino acids
Different combinations can make the same amino acid
Each codon is like a letter of the alphabet.
Different combinations of letters or CODONS
make up words
known as EXONS
a number of EXONS are then translated into proteins
made from EXONS
an EXON made of CODONS
One Gene out of your 20,000 ±
On average 8 to 9 Exons in one gene
but
a variablility of up to 17000
An Inton is a “spacer” between Exons
but
are 10 to 100 times longer
A couple of examples
Protein
Chrom
No
Breast cancer
type 2
susceptibility 13
protein
Cystic fibrosis
transmembrane 7
conductance
regulator
Gene
Length
bps
No of
Exons
Exon
bps
Intron
bps
72,350
BRCA2
83,736
27
11,386
CFTR
202,881
27
4,440
bps = base pairs
198,441
eg: algae
How Proteins are made
The DNA unwinds at each Exon and makes copy .
Each Exon copy is added to the string.
The accumulated is mRNA messenger Ribonucleic acid
How Proteins are made
amino acid
transfer RNA
ribosomal RNA
Long chain of amino acids
Protein folding
Aberrant protein folding:
- leads to neurodegenerative diseases
- is intimately connected with ageing
How DNA folds up
HOW IT WORKS
How a chromosome in DNA replicates
DNA polymerase can only work in one direction
The new strand and the original template join together
short arm
centromere
Long arm
chromatid
chromatid
This is the start of the cell division process
VIDEO
https://www.youtube.com/watch?v=yqESR7E4b_8
Bacteria
¬ Are independent self-replicating DNA based
life forms (160k to 12 million bps)
¬ They exist in almost every environment
¬ The mass of bacteria on earth exceeds that
of plants and animals
¬ They play a vital role in protecting the body
and its functioning
BUT ALSO
¬ In parasitic association with organisms they become pathogens and are
implicated in most diseses and causes of death
VIRUSES
¬ Now thought to be one of the earliest forms
life
¬ Cannot self replicate. Require a host cell.
¬ Contain short strands of RNA or DNA
¬ Outnumber all other forms of 'life' put
together
¬ Are able to transfer genes across the species barrier and are thought to have been
essential in the evolution of life.
¬The fledgling science of gene therapy relies on viruses for precision insertion of
DNA sequencs
INHERITANCE
Ú All humans are over 99.5% genetically identical
Genotype -
is your unique DNA sequence
Phenotype - is your actual physical characteristics which
result from your DNA sequence
Allele -
is a variant found in a particular gene
(for example brown or blue eyes)
they are dominant or recessive,
or often have no effect at all
Ú Identical twins are the same Genotype but are different Phenotypes
EPIGENETICS
The study of genetic effects not entirely encoded
by DNA
¬ Lifestyle
¬ Environment
¬ Health history
¬ Age
Permanent/temporary
Heritable/unique
Damaging/benign
FUTURE of GENETICS
3 billion base pairs and an almost infinite variety of Exons,
plus
epigenetics, protein folding and many other variables
Evolution
by
Natural Selection
Evolution
by
Design??